1. Field of the Invention
The disclosure relates to accounting in a communication system and in particular to accounting in a network between originating and terminating networks.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. Establishment of a communications session generally enables a user to be provided with various services. A session may, for example, be a telephone call between users or multi-way conference session, or a communication session between one or more user equipments and an application server (AS), such as a service provider server.
A communication system typically operates in accordance with a given standard and/or specifications which set out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, a standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined.
A user may access the communication system based on different access technologies. For example, a user may access the communication system via a wireless access network or a fixed line access system. Regardless the access technology, one or more gateway functions are typically provided for interconnecting a plurality of networks. For example, if a requested service is provided by a service provider connected to another network, the service request is routed via one or more networks and gateways there between to the network of the service provider. Thus a communication session may be provided via a plurality of networks. It is also possible to route communication sessions via networks that are operated by different operators. The networks may be provided with own control functions and may be operated relatively independently from each other and based on different standards and protocols.
The so called multimedia services are an example of services that may be offered for a user of a communication system. An example of communication systems enabled to offer multimedia services are known as Internet Protocol (IP) Multimedia networks. IP Multimedia (IM) functionalities can be provided by means of an IP Multimedia Core Network (CN) subsystem, or briefly IP Multimedia subsystem (IMS). The IMS includes various network entities for the provision of the multimedia services. The IMS services are intended to offer, among other services, IP connections for mobile user equipment. The Third Generation Partnership Project (3GPP) has defined a reference architecture for the third generation (3G) core network which will provide the users of user equipment with access to the multimedia services. This core network is divided into three principal domains. These are the Circuit Switched (CS) domain, the Packet Switched (PS) domain and the Internet Protocol Multimedia (IM) domain. It is expected that various types of services are to be provided by means of different Application Servers (AS) over systems such as those based on the IMS.
An IP Multimedia subsystem (IMS) network is typically configured to support the Session Initiation Protocol (SIP). The SIP is developed by the Internet Engineering Task Force (IETF). Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying and terminating sessions with one or more participants (endpoints). SIP was generally developed to allow for initiating a session between two or more endpoints in the Internet by making these endpoints aware of the session semantics. A user connected to a SIP based communication system may communicate with various entities of the communication system based on standardised SIP messages. User equipment or users that run certain applications on the user equipment are registered with the SIP backbone so that an invitation to a particular session can be correctly delivered to these endpoints. To achieve this, SIP provides a registration mechanism for devices and users, and it applies mechanisms such as location servers and registrars to route the session invitations appropriately. Examples of the possible sessions that may be provided by means of SIP signalling include Internet multimedia conferences, Internet telephone calls, and multimedia distribution.
A transit IP Multimedia subsystem (IMS) functionality has also been introduced in the Third Generation Partnership Project (3GPP) specifications. A transit IMS functionality may be provided in a network that is between networks of two other operators. A number of general cases exists in which IMS may be used for a transit network support. In accordance with a possibility an IMS operator provides transit functionality to other network operators. In other words, an operator serves as an IMS session based routing backbone for another networks, for example a public land mobile network (PLMN), a public switched telephone network (PSTN) or an internet protocol (IP) network and provides connectivity to the endpoints of the other networks. Traffic from e.g. a PSTN operator may arrive at an appropriate gateway which may translate it to be in accordance with the SIP, if this is required. The operator then routes the traffic to the destination network depending on the terminating endpoint.
Certain issues relating to charging and accounting of charges in a transit network, however, remain yet unsolved. For example, at the current proposals, SIP session handling mechanisms do no support charging by transit networks. Thus inter-operator accounting may be considerably hindered or even blocked if a transit IP Multimedia subsystem (IMS) is used in a SIP session/transaction. For example, operators providing IMS transit functionality may follow different approaches regarding inter-operator accounting. Another example of a feature where the operators may differ from one another is whether a transit IMS network operator has an intermediary role in the inter-operator accounting or not.